Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

A base station transmits a random access response in response to a random
access request (random access preamble) of a user equipment. The random
access response includes information about a time when the random access
request is transmitted and sequence number information of the random
access request (random access preamble). The user equipment checks
whether the received random access response is the response of the random
access request transmitted by the user equipment, using the information
about the time when the random access request is transmitted and the
sequence number information included in the received random access
response.

Claims:

1. A method of receiving a random access response, the method comprising:
transmitting a random access preamble; and receiving the random access
response corresponding to the random access preamble, wherein the
received random access response includes information of a transmission
time when the random access preamble is transmitted.

2-11. (canceled)

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of the Korean Patent
Application No. 10-2008-0047656, filed on May 22, 2008, which is hereby
incorporated by reference as if fully set forth herein.

[0002] This application also claims the benefit of U.S. Provisional
Application Ser. No. 61/018,492, filed on Jan. 1, 2008, the contents of
which are hereby incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] The present invention relates to a wideband radio access system,
and more particularly, to a method of transmitting and receiving a random
access request (random access preamble) and transmitting and receiving a
random access response in a wideband radio access system.

[0005] 2. Discussion of the Related Art

[0006] In a technology related to a wideband radio access system, each
user equipment may attempt to access the system with a randomly selected
sequence or opportunity in each random access channel (RACH) slot. A base
station detects a random access sequence (or an RACH sequence) and then
transmits a random access response (or an RACH response). Each user
equipment receives the random access response from the base station,
considers a response including its sequence as its response, and performs
a timing advance operation.

[0007] In the technology of this field, each user equipment may attempt to
access the system with a randomly selected sequence or opportunity in
each RACH slot. A base station detects the RACH sequence and then
transmits a response thereof. Each user equipment receives the RACH
response from the base station, considers a response including its
sequence as its response and performs a timing advance operation. At this
time, if an accurate time interval is not present when each user
equipment waits for the response, each user equipment may erroneously
receive a response of another user equipment as its response. This state
is shown in FIG. 1A. FIG. 1A is a view showing an example of an RACH
response (random access response). This state may appear in all RACH
periods. Referring to "3GPP TS 36.211 v.8.1.0, `Evolved Universal
Terrestrial Radio Access (E-UTRA); Physical channels and modulation`,
2007 Dec. 20" regarding to random access in a wideband radio access
system, a table for a random access preamble format, a random access
preamble parameter and random access preamble timing for preamble formats
0 to 3 is described. FIG. 1A shows an RACH slot having a period of 1 ms
and a preamble format of 0.

[0008] In FIG. 1A, a first user equipment 1 attempts access with a
randomly selected sequence 1 in an uplink (UL) subframe 0 (S110). In an
uplink subframe 1, a second user equipment 2 attempts access with a
randomly selected sequence 1 (S120). If a base station detects the
sequences of the two user equipments, the base station transmits
responses of the detected sequences (S130). At this time, the two user
equipments 1 and 2 which attempt access wait for their responses. When
the response of the sequence 1 is reached in an uplink subframe 7, both
the user equipment 1 (UE1) and the user equipment 2 (UE2) may determine
that the response reached in the uplink subframe 7 is the response for
their sequence. In this case, one of the two user equipments erroneously
determines that the response reached in the uplink subframe 7 is its
response. Since the two user equipments perform time synchronization by
the response received in the uplink subframe 7, one user equipment
performs erroneous time synchronization. In addition, since data or a
control signal is transmitted again in uplink using the same resource
indicated by the response, a problem that the two user equipments use the
same resource occurs.

[0009] In FIG. 1 and the description related to FIG. 1, a cell radius is
not considered in order to facilitate the understanding of the problems
of the technology related to the present invention. However, if the cell
radius is actually about 50 km and the propagation speed of an
electromagnetic wave is considered, a random access preamble transmitted
by the user equipment 1 in the uplink subframe 0 may reach the base
station in a downlink subframe 0 or a downlink subframe 1, and a random
access preamble transmitted by the user equipment 2 in the uplink
subframe 1 may reach the base station in a downlink subframe 1 or a
downlink subframe 2. In addition, a random access response transmitted by
the base station in the downlink subframe 1 may reach the user equipment
1 and/or the user equipment 2 in the uplink subframe 1 or an uplink
subframe 2 and a random access response transmitted by the base station
in the downlink subframe 2 may reach the user equipment 1 and/or the user
equipment 2 in the uplink subframe 2 or an uplink subframe 3 (see FIG.
1B).

[0010] Unlike the above example, if a resource available in a time domain
in which the base station transmits the response is not present, a
problem that the response cannot be transmitted on time occurs. In this
case, the response of the RACH slot is not transmitted or is delayed. At
this time, there is a need for a method of distinguishing between a
delayed response and a response which is transmitted on time or between
delayed responses.

[0011] In addition, if responses of several RACH slots are collected and
are simultaneously transmitted, there is a need for a method of
distinguishing between RACH slots.

SUMMARY OF THE INVENTION

[0012] An object of the present invention devised to solve the problem
lies on a method of transmitting and receiving a random access response,
which is capable of preventing a user equipment which attempts to access
using a randomly selected sequence from erroneously receiving a response
for the access of another user equipment, which attempts access with the
same sequence, as a response for its access.

[0013] The object of the present invention can be achieved by providing a
method of transmitting a random access preamble and receiving a random
access response, the method including: at an user equipment, transmitting
the random access preamble; and at the user equipment, receiving the
random access response of the random access preamble, wherein the random
access response received by the user equipment includes time related
information of a time point when the random access preamble corresponding
to the received random access response is transmitted. The time related
information may include a subframe related number at the time point when
the user equipment transmits the random access preamble. The subframe
related number may be a number allocated to a subframe, in which a random
access channel (RACH) slot is present, of subframes. The allocation may
be performed by a modulo operation of the subframe number, in which the
RACH slot is present, of the subframes. The modulo operation may be a
modulo-4 operation. The time related information may be estimated on the
basis of a cell size.

[0014] In another aspect of the present invention, provided herein is a
method of receiving a random access preamble and transmitting a random
access response, the method including: at a base station, receiving the
random access preamble; and at the base station, transmitting the random
access response of the received random access preamble, wherein the
transmitted random access response includes time related information of a
time point when the received random access preamble is transmitted or
delay offset information related to a processing delay time consumed for
transmitting the random access response from when the base station
receives the random access preamble. The transmitted time point may be
estimated by the base station on the basis of a cell size. The received
random access preamble may include time related information of the time
point when the received random access preamble is transmitted, and the
time related information included in the transmitted random access
response may be associated with time related information included in the
received random access request.

[0015] In another aspect of the present invention, provided herein is
method of transmitting a random access preamble and receiving a random
access response, the method including: at a user equipment, transmitting
the random access preamble; and at the user equipment, receiving the
random access response, wherein the receiving of the random access
response at the user equipment is performed in a predetermined time
period including a predetermined time after a time point when the random
access preamble is transmitted, and the predetermined time is a time when
a time obtained by adding a predetermined offset time to a time
corresponding to a half of a hybrid automatic repeat request (HARQ)
process round trip time elapses after the time point when the random
access preamble is transmitted. The random access response may include
delay offset information, and the delay offset information may be used to
change the predetermined time period.

[0016] According to the present invention, it is possible to solve a
problem that a user equipment recognizes a random access response for a
random access request transmitted by another user equipment as a response
for its random access request.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which are included to provide a further
understanding of the invention, illustrate embodiments of the invention
and together with the description serve to explain the principle of the
invention.

[0018] In the drawings:

[0019] FIGS. 1A and 1B are views showing an example of a random access
response.

[0020] FIG. 2A is a view showing an example of a frame structure used in a
wideband radio access system.

[0021] FIG. 2B is a view showing an example of a random access preamble
format.

[0022] FIGS. 3A and 3B are views showing a random access response
including time information according to an embodiment of the present
invention.

[0023] FIG. 4 is a flowchart illustrating a method of transmitting and
receiving a random access request and a random access response according
to another embodiment of the present invention.

[0024] FIGS. 5A and 5B are views showing a random access response
including time information if an RACH slot has a period of 2 ms,
according to another embodiment of the present invention.

[0025] FIGS. 6A and 6B are views showing a delayed random access response
if an RACH slot has a period of 2 ms, according to the embodiment of the
present invention.

[0026] FIGS. 7A and 7B are views explaining renumbering and grouping
according to another embodiment of the present invention.

[0027] FIG. 8 is a flowchart in detail illustrating an internal process of
a step S420 of FIG. 4 according to another embodiment of the present
invention.

[0028]FIG. 9 is a flowchart illustrating a method of transmitting and
receiving a random access request and a random access response according
to another embodiment of the present invention.

[0029] FIG. 10 is a view in detail showing an internal process of a step
S920 (S920') of FIG. 9.

[0030] FIG. 11 is a view explaining the principle of an automatic repeat
request (ARQ).

[0031] FIG. 12 is a view explaining the principle of a hybrid automatic
repeat request (HARQ).

[0032] FIG. 13 is a view showing a detailed example of a HARQ process
according to another embodiment of the present invention.

[0033] FIG. 14 is a flowchart illustrating a method of transmitting and
receiving a random access request and a random access response according
to another embodiment of the present invention.

[0034] FIG. 15 is a view explaining the classification of channels
according to layers in a wideband radio access system.

[0035] FIG. 16 is a view explaining the classification of channels
according to layers and areas.

DETAILED DESCRIPTION OF THE INVENTION

[0036] Reference will now be made in detail to the preferred embodiments
of the present invention, examples of which are illustrated in the
accompanying drawings. The following embodiments are examples applied to
a wideband radio access system, which may refer to "3GPP TS 36.211
v.8.1.0, `Evolved Universal Terrestrial Radio Access (E-UTRA); Physical
channels and modulation`, 2007 Dec. 20" regarding to random access in a
wideband radio access system.

[0037] In the wideband radio access system, a "channel" refers to a
passage allocated to transmitter and receiver and indicates a logical
signal passage rather than a physical transmission path. Accordingly,
several channels may exist in one transmission path.

[0038] In an asynchronous wideband code division multiplexing access
(WCDMA), three channels are defined according to layers. A first channel
is a logical channel between a radio link control (RLC) layer and a
medium access control (MAC) layer, and is classified depending on which
type of information is included, that is, the "type of information". A
second transport channel is a channel between the MAC layer and a
physical layer, is classified according to the "characteristics of
delivery information", and is largely classified into a dedicated
transport channel and a common transport channel. A third physical
channel is a channel transmitted via an actual antenna and is classified
according to the "radio resource and, more particularly, efficiency of a
code and RF output" (see FIGS. 15 and 16). In the RLC layer for providing
transport reliability, retransmission is performed in the unit of logical
channels. That is, when an error occurs in a receiver side, logical
channel retransmission is performed in the information units
(transmission time intervals (TTIs)), instead of the frame units
configured in the physical layer.

[0039] The transport channel is the delivery channel between the physical
layer and an upper layer and is defined according to the characteristics
of transport data and transmitting methods. The transport channel
transmits data received from the logical channel, but the logical channel
and the transport channel do not one-to-one correspond to each other.
Several logical channels may be transmitted using one transport channel.
Accordingly, the MAC layer between the logical channel and the transport
channel perform mapping between the logical channel and the transport
channel.

[0040] Similar to the logical channel, the transport channel is considered
as the flow of data rather than the physical channel. In particular,
since all protocols are located at the same location in the user
equipment, the transport channel of the user equipment is internally
defined between the MAC layer and the physical layer. Since the physical
layer is located at a node B in a universal mobile telecommunication
system (UMTS) terrestrial radio access network (UTRAN), an appropriate
interface should be defined for data exchange with the MAC layer located
at a radio network controller (RNC).

[0041] The transport channel is classified into the dedicated transport
channel and the common transport channel according to the characteristics
of the delivery information. A dedicated channel (DCH) belongs to the
dedicated transport channel, and a broadcasting channel (BCH), a forward
access channel (FACH), a paging channel (PCH), a random access channel
(RACH), a downlink shared channel (DSCH), a common packet channel (CPCH),
and a high speed-downlink shared channel (HS-DSCH) belong to the common
transport channel.

[0042] The RACH transmits control information such as short packet data
such as a short messaging service (SMS) and call set-up in uplink, and
operates by a process similar to a synchronous random access channel on
the basis of a slotted ALOHA random access scheme. Accordingly, collision
risk with the signal of another user equipment may occur, and an
open-loop power control is used. While a transmission rate of 9.6 kbps is
defined in the synchronous CDMA system, a transmission rate of up to 120
kbps is defined in an asynchronous system. However, the transmission rate
is actually restricted to about 15 kbps.

[0043] The physical channel is transmitted via the actual antenna and
various types of information are transmitted via one physical channel or
several physical channels. Since some overhead physical channels are used
for aiding the transmission and reception of the physical channels
regardless of the upper layer, they are generated by a base station
without a direct mapping relation with the transport channel. Among the
transport channels, the RACH is mapped to a physical random access
channel (PRACH) of the physical channel.

[0044] In uplink random access, a user equipment which does not access a
base station uses a slotted ALOHA random access scheme in order to access
the base station, and gradually increases and repeatedly transmits a
probe output until access becomes successful when a probe (an action for
checking and finding something) transmission fails. In the WCDMA system,
an Acquisition Indication sense multiple access (AiSMA) scheme of
transmitting only a preamble part in each probe, receiving information
that synchronization acquisition of an access preamble is performed from
the base station via an acquisition indication channel (AICH) and
transmitting a message part is employed. Accordingly, since the
transmission time of the random access probe in the WCDMA system is
extremely shorter than that of the synchronous system, a base station
reception noise phenomenon due to the probes which fail in the access to
the base station is remarkably improved. Information about subgroups and
codes available for a random access preamble part is specified according
to access service rating via a system information block (SIB) 5 message
from a radio resource management layer which is an upper layer, and
information about a transmission format of a message part and a system
frame number is received from the MAC layer. A random access channel is
used to perform an operation related to a request for the set-up of the
call to the base station and to transmit short one-way packet data of one
or two frames in uplink.

[0045] The message part transmitted after an ACK signal for a preamble
signal is received has a length of 10 msec or 20 msec, and a substantial
data part and a control part are multiplexed to an I/Q channel, are
BPSK-modulated and are simultaneously transmitted.

[0046] In order to minimize a probability that RACH signals of several
user equipments collide, the transmission of the RACH signals is started
in respective access slots specified to the user equipments. The access
slot number is uniquely specified in an upper layer. Parameters related
to the RACH are broadcasted to all the reception-standby user equipments
via the SIB 5 of the BCH.

[0047] FIG. 2A is a view showing an example of a frame structure used in a
wideband radio access system.

[0048] In "3GPP TS 36.211 v.8.1.0, `Evolved Universal Terrestrial Radio
Access (E-UTRA); Physical channels and modulation`, 2007 Dec. 20", a
physical channel for an evolved UTRA is described. Two frame structures
may be used. A first frame structure (see FIG. 2A) is applicable to a
full duplex frequency division duplex (FDD) and a half duplex FDD. Each
radio frame has a length of 10 ms and is configured by 20 slots each
having a length of 0.5 ms. The slots have numbers of 0 to 19. One
subframe is configured by two continuous slots. In the FDD, 10 subframes
are used for an uplink transmission and a downlink transmission during 10
ms.

[0049] FIG. 2B is a view showing an example of a random access preamble
format.

[0050] As shown in FIG. 2B, a physical layer random access preamble
includes a cyclic prefix (CP) having a length of TCP and a sequence
part having a length of TSEQ. Parameters are shown in Table 1 and
are decided by the frame structure and the random access configuration.
The preamble format is controlled by the upper layer.

[0051] With respect to the preamble formats 0 to 3, a maximum of one
random access resource exists per subframe. Table 2 shows subframes for
allowing a random access preamble transmission in the given
configuration. If it is assumed that a timing advance is zero, the start
of the random access preamble will be aligned in parallel to the start of
an uplink subframe corresponding to a user equipment (terminal). In Table
2, the random access channel has a period of 1 ms to 20 ms.

[0052] In the following description, the RACH configuration having the
period of 1 ms will be described. However, the present invention is not
limited to such an RACH period. In addition, since the effect of the
present invention is further increased when the period is short, the
present invention may be used only in a specific RACH configuration
having a short period. In addition, although the 3GPP LTE system is used
for convenience of description, the present invention is not limited to
this. For example, the present invention is applicable to a ranging
channel of the IEEE 802.16 (hereinafter, referred to as 802.16). In other
words, an RACH response of the LTE described in the present invention may
be analyzed as a ranging response of the 802.16.

[0053] FIG. 3A is a view showing a random access response including time
information according to an embodiment of the present invention.

[0054] In the embodiment of the present invention described in FIG. 3A,
since a method of transmitting a random access response including time
information is used, it is possible to prevent the random access response
from being erroneously received. In this case, since additional
information is further transmitted, signaling overhead may slightly
occur. For example, as shown in FIG. 3A, when the base station transmits
the random access response, it is possible to transmit the uplink
subframe number of the time point when the user equipment transmits a
random access request (random access preamble) (hereinafter, the uplink
subframe number of an uplink subframe 0 is denoted by "0"). Like the
embodiment described in FIG. 3A, it is assumed that each subframe has a
length of 1 ms in a time domain. In addition, it is assumed that an RACH
slot for transmitting the random access preamble has a period of 1 ms. A
user equipment 1 may transmit a random access preamble having a randomly
selected sequence number 1 in an uplink subframe 0 (S310). A user
equipment 2 may transmit a random access preamble having a sequence
number 1, which is randomly selected but is identical to the sequence
transmitted by the user equipment 1, in an uplink subframe 1 (S320). A
base station may receive the random access sequence transmitted by the
user equipment 1 in a downlink subframe 3 and then transmit a random
access response thereof (S330). This random access response may include
information about the sequence number 1 and the uplink subframe 0.
Thereafter, the base station may receive the random access sequence
transmitted by the user equipment 2 in a downlink subframe 4 and then
transmit a random access response thereof (S340). This random access
response may include information about the sequence number 1 and the
uplink subframe 1. The user equipment 1 and the user equipment 2 may
receive the random access response of the random access preamble
transmitted by the user equipment 1 in an uplink subframe 7. Thereafter,
the user equipment 1 and the user equipment 2 may check whether the
uplink subframe number included in the received random access response is
identical to any one of the uplink subframe numbers of the random access
preambles transmitted by the user equipment 1 and the user equipment 2.
If the uplink subframe number included in the random access response
received by the user equipment 1 is identical to the uplink subframe
number of the random access preamble transmitted by the user equipment 1,
it may be determined that the random access response received by the user
equipment 1 is the response of the random access transmitted by the user
equipment 1. However, if the uplink subframe number included in the
random access response received by the user equipment 1 is not identical
to the uplink subframe number of the random access preamble transmitted
by the user equipment 1, it may be determined that the random access
response received by the user equipment 1 is not the response of the
random access transmitted by the user equipment 1. Similarly, if the
uplink subframe number included in the random access response received by
the user equipment 2 is identical to the uplink subframe number of the
random access preamble transmitted by the user equipment 2, it may be
determined that the random access response received by the user equipment
2 is the response of the random access transmitted by the user equipment
2. However, if the uplink subframe number included in the random access
response received by the user equipment 2 is not identical to the uplink
subframe number of the random access preamble transmitted by the user
equipment 2, it may be determined that the random access response
received by the user equipment 2 is not the response of the random access
transmitted by the user equipment 2.

[0055] In FIG. 3A and the description related to FIG. 3A, a cell radius is
not considered in order to facilitate the understanding of the problems
of the technology related to the present invention. However, if the cell
radius is actually about 50 km and the propagation speed of an
electromagnetic wave is considered, the random access preamble
transmitted by the user equipment 1 in the uplink subframe 0 may reach
the base station in a downlink subframe 0 or a downlink subframe 1, and
the random access preamble transmitted by the user equipment 2 in the
uplink subframe 1 may reach the base station in a downlink subframe 1 or
a downlink subframe 2. Similarly, a random access response transmitted by
the base station in the downlink subframe 1 may reach the user equipment
1 and/or the user equipment 2 in the uplink subframe 1 or an uplink
subframe 2 and a random access response transmitted by the base station
in the downlink subframe 2 may reach the user equipment 1 and/or the user
equipment 2 in the uplink subframe 2 or an uplink subframe 3 (see FIG.
3B).

[0056] FIG. 4 is a flowchart illustrating a method of transmitting and
receiving a random access between a user equipment 1, a user equipment 2
and a base station, according to another embodiment of the present
invention.

[0057] The user equipment 1 and the user equipment 2 select random access
channel parameters, such as a PRACH configuration and a preamble format,
in steps S410 and S410', respectively. As the PRACH configuration and the
preamble format, one of the configurations shown in Table 1 and Table 2
may be selected. The user equipment 1 and the user equipment 2 may decide
the sequence number of the random access preamble to be transmitted and
apply it to the preamble, respectively. The random access preamble
sequence numbers transmitted by the user equipment 1 and the user
equipment 2 may be identical or different. In this embodiment, it is
assumed that the sequence numbers transmitted by the user equipment 1 and
the user equipment 2 are identical to "1". The user equipment 1 and the
user equipment 2 extract and store the uplink subframe numbers at time
points when the random access preambles are transmitted, in steps S420
and S420', respectively. The time point when the random access preamble
is transmitted by the user equipment 1 may be different from the time
point when the random access preamble is transmitted by the user
equipment 2. Hereinafter, the respective uplink subframe numbers stored
by the user equipment 1 and the user equipment 2 are denoted by sf_F_N.
In this embodiment, the random access preambles RAP1 and RAP2 transmitted
by the user equipment 1 and the user equipment 2 are transmitted at time
points corresponding to the uplink subframe numbers sf_F_N=1 and
sf_F_N=2, respectively. The user equipment 1 and the user equipment 2
transmit the random access preambles in steps S430 and S430',
respectively.

[0058] If the base station 3 receives the random access preambles (e.g.,
RAP1 and RAP2), the base station 3 extracts the sequence numbers of the
received random access preambles and estimates the uplink subframe
numbers sf_F_N=j, which might be transmitted by the received random
access preambles, in consideration of the cell radius (cell size). The
base station 3 includes the estimated information in the random access
responses of the received random access preambles (S440). Thereafter, the
base station 3 transmits the random access responses (S450). The
transmitted random access responses may reach the user equipment 1 and
the user equipment 2. In this embodiment, the base station 3 transmits
the random access response of the random access preamble transmitted by
the user equipment 1 before transmitting the random access response of
the random access preamble transmitted by the user equipment 2. The user
equipment 1 and the user equipment 2 receive the respective random access
responses transmitted in the step S450. The user equipment 1 and the user
equipment 2 extract the uplink subframe numbers included in the received
random access responses and compare the extracted subframe numbers with
the uplink subframe numbers stored in the step S420 (step S420'), in the
steps S460 and S460'. In the user equipment 1, since the uplink subframe
number sf_R_N=1 included in the received random access response is
identical to the stored uplink subframe number sf_F_N=1 of the random
access preamble transmitted by the user equipment 1, it may be determined
that the received random access response is the response of the random
access preamble transmitted by the user equipment 1. In the user
equipment 2, since the uplink subframe number sf_RN=1 included in the
received random access response is different from the stored uplink
subframe number sf_F_N=2 of the random access preamble transmitted by the
user equipment 2, it may be determined that the received random access
response is not the response of the random access preamble transmitted by
the user equipment 2. Each user equipment may further use sequence
information included in the received random access response as well as
the uplink subframe number included in the received random access
response, in order to check whether the random access response received
by each user equipment is the response of the random access preamble
transmitted by each user equipment. If both the sequence information and
the uplink subframe number included in the random access response
received by any user equipment are identical to the sequence information
included in the random access preamble transmitted by the user equipment
and the uplink subframe number at the time point when the user equipment
transmits the random access preamble, it may be determined that the
received random access response is the response of the random access
preamble transmitted by the user equipment.

[0059] FIG. 5A shows the case where each subframe has a length of 1 ms in
a time domain and an RACH slot for transmitting a random access preamble
has a period of 2 ms.

[0060] A user equipment 1 transmits a random access preamble having a
randomly selected sequence number 1 in an uplink subframe 0 (S510). A
user equipment 2 transmits a random access preamble having a sequence
number 1, which is randomly selected but is identical to the sequence
transmitted by the user equipment 1, in an uplink subframe 2 (S520). A
base station receives the random access sequence transmitted by the user
equipment 1 in a downlink subframe 3 and then transmits a random access
response thereof (S530). This random access response (S530) includes the
sequence number 1 and the uplink subframe number sf_F_N=0 included in the
random access preamble received in the downlink subframe 3, which is
estimated by the base station in consideration of a cell radius (cell
size). Thereafter, the base station receives the random access sequence
transmitted by the user equipment 2 in a downlink subframe 5 and then
transmits a random access response thereof (S540). This random access
response (S540) may include the sequence number 1 and the uplink subframe
number sf_F_N=2 included in the random access preamble received in the
downlink subframe 5, which is estimated by the base station in
consideration of a cell radius (cell size).

[0061] The embodiment of FIG. 5A is different from the embodiment of FIG.
3A in that the random access sequence is transmitted only in the uplink
subframe having an even number. That is, the random access sequence is
transmitted only in the uplink subframes 0, 2, 4, 6 and 8 which is
hatched in FIG. 5A. Accordingly, in order to enable the base station to
estimate the uplink subframe numbers so as to represent the numbers by
binary numbers, four signaling bits are necessary. If the original uplink
subframe numbers Original={0, 2, 4, 6, 8} are renumbered to
Renumbered={0, 1, 2, 3, 4}, the numbers can be represented using only
three signaling bits. Thus, it is possible to reduce the number of
signaling bits. This concept is applicable to the embodiment of FIG. 4.

[0062] Although one RACH channel is present per subframe in the present
invention, this is exemplary for convenience of description and the
present invention is applicable to the case where several RACH channels
are present per subframe. For example, the RACH channel number and the
subframe number can be signaled on a frequency within a subframe.
Alternatively, the numbers may be two-dimensionally allocated and
signaled in frequency and time domains. An RACH channel may be numbered
on a frequency within a subframe and an RACH channel of a next subframe
may be then numbered subsequent to that number. In contrast, an RACH
channel is first numbered on a subframe and an RACH channel may be then
numbered on another frequency domain subsequent to that number.

[0063] In the invention, the RACH subframe number may be defined in the
unit of frames or superframes.

[0064] In FIG. 5A and the description related to FIG. 5A, a cell radius is
not considered in order to facilitate the understanding of the problems
of the technology related to the present invention. However, if the cell
radius is actually about 50 km and the propagation speed of an
electromagnetic wave is considered, the random access preamble
transmitted by the user equipment 1 in the uplink subframe 0 may reach
the base station in a downlink subframe 0 or a downlink subframe 1, and
the random access preamble transmitted by the user equipment 2 in the
uplink subframe 2 may reach the base station in a downlink subframe 2 or
a downlink subframe 3. Similarly, a random access response transmitted by
the base station in the downlink subframe 1 may reach the user equipment
1 and/or the user equipment 2 in the uplink subframe 1 or an uplink
subframe 2, and a random access response transmitted by the base station
in the downlink subframe 3 may reach the user equipment 1 and/or the user
equipment 2 in the uplink subframe 3 or an uplink subframe 4 (see FIG.
5B).

[0065] FIG. 6A is a view showing a delayed random access response if an
RACH slot has a period of 2 ms, in the embodiment of FIG. 5A.

[0066] That is, the random access response of the uplink subframe 0 is
delayed. When a base station receives a random access preamble in a
downlink subframe 3 (S610), the base station may not have a resource
which will be transmitted in downlink. This may occur in various cases.
For example, if a resource is used for a dedicated multicast broadcast
single frequency network (MBSFN), a unicast downlink resource cannot be
allocated. In contrast, although a resource is not used for a special
purpose, all resources may be used for other control signals and data
signals at a specific time. In this case, the transmission of the random
access response may be delayed. In addition, several random access
responses may be simultaneously transmitted by one resource. Accordingly,
time information (that is, delay offset information) related to the
delayed time is preferably included in the random access response. As the
time information (or the time related information), other information
related to the time and/or the subframe number may be used.

[0067] In FIG. 6A and the description related to FIG. 6A, a cell radius is
not considered in order to facilitate the understanding of the problems
of the technology related to the present invention. However, if the cell
radius is actually about 50 km and the propagation speed of an
electromagnetic wave is considered, the random access preamble
transmitted by the user equipment 1 in the uplink subframe 0 may reach
the base station in a downlink subframe 0 or a downlink subframe 1, and
the random access preamble transmitted by the user equipment 2 in the
uplink subframe 2 may reach the base station in a downlink subframe 2 or
a downlink subframe 3. Similarly, a random access response transmitted by
the base station in the downlink subframe 3 may reach the user equipment
1 and/or the user equipment 2 in the uplink subframe 3 or an uplink
subframe 4 (see FIG. 6B).

[0068] FIGS. 7A and 7B are views explaining renumbering and grouping
according to another embodiment of the present invention.

[0069] Up to now, the uplink subframe number or the renumbered uplink
subframe number was used as the time information included in the random
access response. However, a grouping method may be used when the uplink
subframe number is renumbered. As the grouping method, a modulo operation
and/or various known methods may be used (the modulo operation indicates
an operation for obtaining a remainder when a number is divided by
another number). For example, a modulo-4 operation indicates an operation
for obtaining a remainder when any number is divided by 4 as a result
value. For example, the subframe number may be renumbered so as to be
repeated in a period of 10 ms or less. For example, while 4-bit signaling
is necessary if a fifteenth PRACH configuration of Table 2 is used, 2-bit
signaling is necessary if the uplink subframe number is subjected to the
modulo-4 operation. Application examples may be made using various PRACH
configurations of Table 2. FIGS. 7A and 7B show one of these examples. In
FIGS. 7A and 7B, in a configuration in which the length of an uplink
subframe is 1 ms and RACH slots are repeated in a period of 2 ms, the
uplink subframe numbers in which the RACH slots are present are
renumbered. The uplink subframe numbers are grouped and repeated by the
modulo-4 operation.

[0070] FIG. 8 is a flowchart in detail illustrating an internal process of
a step S420 of FIG. 4, in which the embodiment of FIG. 7 is applied to
the embodiment of FIG. 4.

[0071] In a step S810, subframes in which an RACH slot is present are
detected. In a step S820, numbers are reallocated to only the uplink
subframes in which the RACH slot is present. In a step S830, the
reallocated number of an uplink subframe at a time point when a random
access will be transmitted is decided. In a step S840, the decided
reallocated number is stored. Although, in this embodiment, the RACH
slots are present only in even-numbered frames, the RACH slots may be
present in any numbered frames. That is, the reallocation of the numbers
in the step S830 may use the grouping method. In more detail, the modulo
operation may be used.

[0072]FIG. 9 is a flowchart illustrating a method of transmitting and
receiving a random access request and a random access response according
to another embodiment of the present invention, that is, a method of
transmitting and receiving a random access between a user equipment 1, a
user equipment 2 and a base station.

[0073] The user equipment 1 and the user equipment 2 may select random
access channel parameters such as a PRACH configuration and a preamble
format in steps S910 and S910', respectively. As the PRACH configuration
and the preamble format, one of the configurations shown in Table 1 and
Table 2 may be selected. The user equipment 1 and the user equipment 2
decide the sequence numbers of the random access preambles to be
transmitted and apply to the random access preambles, respectively. In
this embodiment, the random access preamble sequence numbers transmitted
by the user equipment 1 and the user equipment 2 may be identical or
different. The user equipment 1 and the user equipment 2 extract the
uplink subframe numbers at time points when the random access preambles
are transmitted and include the extracted uplink subframe numbers in the
random access preambles to be transmitted, in steps S920 and S920',
respectively. The time point when the random access preamble is
transmitted by the user equipment 1 may be different from the time point
when the random access preamble is transmitted by the user equipment 2.
Hereinafter, the respective uplink subframe numbers included in the
random access preambles transmitted by the user equipment 1 and the user
equipment 2 are denoted by sf_F_N. In this embodiment, the random access
preambles RAP1 and RAP2 transmitted by the user equipment 1 and the user
equipment 2 are transmitted at time points corresponding to the uplink
subframe numbers sf_F_N=1 and sf_F_N=2, respectively. The user equipment
1 and the user equipment 2 transmit the random access preambles in steps
S930 and S930', respectively. In this embodiment, it is assumed that both
the random access preambles transmitted by the user equipment 1 and the
user equipment 2 have a sequence number 1.

[0074] If the base station 3 receives the random access preambles (e.g.,
RAP1 and RAP2), the base station 3 may extract the sequence numbers and
the uplink subframe number sf_F_N=j included in the received random
access preambles and include the extracted information in the random
access responses of the received random access preambles (S940).
Hereinafter, the uplink subframe number included in the random access
response is denoted by sf_R_N. Thereafter, the base station 3 transmits
the random access response RAR1 (S950). The transmitted random access
response RAR1 may reach the user equipment 1 and the user equipment 2. In
this embodiment, the base station 3 may transmit the random access
response RAR1 of the random access preamble transmitted by the user
equipment 1 before transmitting the random access response RAR2 of the
random access preamble transmitted by the user equipment 2. The user
equipment 1 and the user equipment 2 receive the respective random access
responses RAR1 transmitted in the step S950. The user equipment 1 and the
user equipment 2 extract the uplink subframe number included in the
received random access responses RAR1 and compare the extracted uplink
subframe number with the uplink subframe numbers included in the
respective random accesses transmitted by the user equipments, in the
steps S960 and S960'. In the user equipment 1, since the uplink subframe
number sf_R_N=1 included in the received random access response RAR1 is
identical to the uplink subframe number sf_F_N=1 of the random access
preamble RAP1 transmitted by the user equipment 1, it may be determined
that the received random access response RAR1 is the response of the
random access preamble RAP1 transmitted by the user equipment 1. In the
user equipment 2, since the uplink subframe number sf_R_N=1 included in
the received random access response RAR1 is different from the uplink
subframe number sf_F_N=2 of the random access preamble RAP2 transmitted
by the user equipment 2, it may be determined that the received random
access response RAR1 is not the response of the random access preamble
RAP2 transmitted by the user equipment 2. Each user equipment may further
use sequence information included in the received random access response
as well as the uplink subframe number included in the received random
access response, in order to check whether the random access response
received by each user equipment is the response of the random access
preamble transmitted by each user equipment. If both the sequence
information and the uplink subframe number included in the random access
response received by any user equipment are identical to the sequence
information and the uplink subframe number included in the random access
preamble transmitted by the user equipment, it may be determined that the
received random access response is the response of the random access
preamble transmitted by the user equipment.

[0075] FIG. 10 is a view in detail showing an internal process of the step
S920 (S920') of FIG. 9.

[0076] The user equipments 1 and 2 decide the uplink subframe numbers at
the time point when the random access preambles are transmitted.
Thereafter, the user equipments 1 and 2 add the uplink subframes numbers
decided in the step S1010 to the preambles to be transmitted, in a step
S1020. FIGS. 11, 12 and 13 are views facilitating the understanding of
the other embodiments of the present invention, which show the principle
of an ARQ, the principle of a HARQ and a detailed example of a HARQ
process, respectively.

[0077] In the other embodiments of the present invention, a user equipment
waits for a response at a predetermined time period. The user equipment
which transmits a random access preamble can previously know a time point
when a response of the random access preamble transmitted by the user
equipment is transmitted, on the basis of the predetermined time period.

[0078] For example, the predetermined time period may be decided in
association with HARQ timing. The HARQ is a hybrid technology of an ARQ
technology of an MAC layer and a channel coding technology of a physical
layer. The ARQ is a closed-loop error correction method based on
feedback. If an error occurs in the physical layer in spite of making an
effort to suppress the occurrence of the error in a transmission by
forward error correction (FEC), a packet in which the error occurs is
retransmitted by the ARQ in an RLC layer. As a result, when data is
transmitted to the RLC layer in uplink, information may be restored by
only packets without an error.

[0079] FIG. 11 is a view explaining the principle of the ARQ. If an error
occurs when a packet P1 transmitted by a transmitter Tx is received
by a receiver Rx (S1110), the receiver Rx transmits a negative
acknowledgement (NAK) signal (S1120). The transmitter Tx which receives
the NAK signal retransmits the same packet P1 as the packet P1
in which the error occurs upon transmission (S1130). If the receiver Rx
confirms that an error does not occur in the retransmitted packet, the
receiver Rx transmits an ACK signal to the transmitter Tx (S1140). The
transmitter Tx which receives the ACK signal transmits a new packet
P2 (S1150).

[0080] FIG. 12 is a view explaining the principle of the HARQ. The HARQ is
different from the ARQ in that the channel coding of the physical layer
is combined to the ARQ. If an error occurs when a receiver Rx receives a
packet P1A transmitted by a transmitter Tx (S1210), the receiver Rx
transmits an NAK signal (S1220). The transmitter Tx which receives the
NAK signal transmits a packet P1B (S1230). In FIG. 12, the packet
P1A and the packet P1B are made of the same information bits,
that is, the same channel encoder input packet P1A and are identical
or slightly different. In the HARQ, although an error occurs in the
packet P1A which is first transmitted, since the packet P1A has
any information amount, the packet P1A is stored without being
discarded until the retransmitted signal is received and is soft-combined
with the retransmitted signal P1B or is demodulated using another
method. A method of utilizing packets in which errors occur and newly
retransmitted packets includes a chase combining (CC) method and an
incremental redundancy (IR) method.

[0081] Each user equipment can estimate a random access response location
on the basis of HARQ timing at a time location of the RACH slot
transmitted by the user equipment and receive only a downlink signal in a
specific time location section. For example, like FIG. 13 showing the
example of the HARQ process, if it is assumed that a time consumed for
performing the HARQ process is 1 ms and the number of HARQ processes is
8, a time consumed for, at the user equipment, processing a signal
transmitted from a base station in downlink and, at the base station,
processing the signal transmitted by the user equipment in uplink is 8
ms. In FIG. 13, Tprop denotes a propagation delay time. A half of a
HARQ round trip time or a half of the total number of HARQ processes is
consumed for receiving a response of a transmitted signal excluding the
processing time of the received signal.

[0082] The user equipment which attempts random access may wait for a half
of the HARQ round trip time or a half of the total number of HARQ
processes from a time point when a random access preamble is transmitted,
and wait for a response within a predetermined time period from a time
point when a half of the HARQ round trip time or a half of the total
number of HARQ processes elapses. Alternatively, a method of applying an
offset (delay offset) in consideration of a difference between a data
processing time and a random access processing time may be used. For
example, a method of receiving a downlink signal by the user equipment at
a location separated from a time determined by the HARQ round trip time
or the total number of HARQ processes by one subframe. This offset may be
represented by adding or subtracting a predetermined number and may be
represented by a multiple of the number of HARQ processes.

[0083] If the RACH having a length of 2 ms or 3 ms is transmitted in the
above method, a method of estimating a time for waiting for a response
from a time location for a start time location of an RACH slot is
possible. Alternatively, a method of estimating a time for waiting for a
response from a time location for an end time location of an RACH slot is
possible.

[0084] It is possible to prevent each user equipment to erroneously
receive a response for another user equipment as its response using a
predetermined response reception time location. If this method is used,
signaling overhead is no longer included in random data in which overhead
is transmitted and received.

[0085] FIG. 14 is a flowchart illustrating a method of transmitting and
receiving a random access between a user equipment 1, a user equipment 2
and a base station, according to an embodiment of the present invention.

[0086] The user equipment 1 and the user equipment 2 select random access
channel parameters, such as a PRACH configuration and a preamble format,
in steps S1410 and S1410', respectively. As the PRACH configuration and
the preamble format, one of the configurations shown in Table 1 and Table
2 may be selected. The user equipment 1 and the user equipment 2 may
decide the sequence numbers of the random access preambles to be
transmitted and apply it to the random access preambles, respectively. In
this embodiment, the random access preamble sequence numbers transmitted
by the user equipment 1 and the user equipment 2 may be identical or
different. The user equipment 1 and the user equipment 2 decide default
times, in which the random access responses of the random access
preambles to be transmitted will be received, and default uplink subframe
sections in advance. The default times or the default uplink subframe
sections may be changed when processing delay occurs in the base station.
This change may be, although described below, performed by, at the base
station, transmitting a random access response in a state of including
information about a processing delay time when processing delay occurs in
the base station. The time point when the random access preamble is
transmitted by the user equipment 1 may be different from the time point
when the random access preamble is transmitted by the user equipment 2.
In this embodiment, the random access preambles RAP1 and RAP2 transmitted
by the user equipment 1 and the user equipment 2 are transmitted at time
points corresponding to the uplink subframe numbers sf_F_N=1 and
sf_F_N=2, respectively. The user equipment 1 and the user equipment 2
transmit the random access preambles in steps S1430 and S1430',
respectively.

[0087] If the base station 3 receives the random access preambles (e.g.,
RAP1 and RAP2), the base station 3 transmits a random access response
RAR1 of the received random access preambles. At this time, as described
above in association with FIG. 7, if the base station uses all resources
for other processes and thus cannot allocate the resources with respect
to the random access request, processing delay may occur when the random
access response is transmitted. If such processing delay occurs, the base
station 3 may include information about the processing delay time (timing
offset) in the random access response (S1440). Thereafter, the base
station transmits a random access response RAR1 (S1450). The transmitted
random access response may reach both the user equipment 1 and the user
equipment 2. In this embodiment, the base station 3 transmits the random
access response RAR1 of the random access preamble transmitted by the
user equipment 1 before transmitting the random access response RAR2 of
the random access preamble transmitted by the user equipment 2. The user
equipment 1 and the user equipment 2 receive the respective random access
responses transmitted in the steps S1460 and S1460'. The user equipment 1
and the user equipment 2 check whether the received random access
responses are received at the default times set in the steps S1460 and
S1460', respectively. Hereinafter, the step S1460 of the user equipment 1
will be described.

[0088] It is assumed that the received random access response is received
at the default time set by the user equipment 1. At this time, the
received random access response may be or may not be the response of the
random access preamble transmitted by the user equipment 1. If the offset
included in the received random access response is 0 (zero), it is
indicated that the processing delay does not occur in the base station 3.
Accordingly, it may be determined that the random access response
received at the default time set by the user equipment 1 is the response
of the random access preamble transmitted by the user equipment 1. In
contrast, if the offset included in the received random access response
is not 0 (zero), it is indicated that the processing delay occurs in the
base station. Accordingly, it may be determined that the random access
response received at the default time set by the user equipment 1 is not
the response of the random access preamble transmitted by the user
equipment 1.

[0089] Subsequently, the step S1460 of the user equipment 1 will be
described. It is assumed that the received random access response is not
received at the default time set by the user equipment 1. At this time,
the received random access response may be or may not be the response of
the random access preamble transmitted by the user equipment 1. If the
offset included in the received random access response is 0 (zero), it is
indicated that the processing delay does not occur in the base station 3.
Accordingly, the user equipment 1 should receive the random access
response at the default time set by the user equipment 1. Thus, it may be
determined that the received random access response is not the response
of the random access preamble transmitted by the user equipment 1. In
contrast, if the offset included in the received random access response
is not 0 (zero), it is indicated that the processing delay occurs in the
base station. Accordingly, it may be determined that the random access
response received at the default time set by the user equipment 1 is the
response of the random access preamble transmitted by the user equipment
1. It is assumed that the user equipment 1 receives the random access
response after j sections (or the number of subframes or the time) from a
time decided in the step S1420. At this time, the offset included in the
received random access response corresponds to the j sections, it is
determined that the received random access response is the response of
the random access preamble transmitted by the user equipment 1. In
contrast, if the offset included in the received random access response
does not correspond to the j sections, it is determined that the received
random access response is not the response of the random access preamble
transmitted by the user equipment 1.

[0090] The above-described embodiments are proposed by combining
constituent components and characteristics of the present invention
according to a predetermined format. The individual constituent
components or characteristics should be considered to be optional factors
on the condition that there is no additional remark. If required, the
individual constituent components or characteristics may not be combined
with other components or characteristics. Also, some constituent
components and/or characteristics may be combined to implement the
embodiments of the present invention. The order of operations to be
disclosed in the embodiments of the present invention may be changed to
another. Some components or characteristics of any embodiment may also be
included in other embodiments, or may be replaced with those of the other
embodiments as necessary. It will be apparent to those skilled in the art
that unrelated claims are combined so as to configure embodiments or are
included in new claims by amendments after an application.

[0091] The above-mentioned embodiments of the present invention are
disclosed on the basis of a data communication relationship between a
base station and a mobile station. In this case, the base station is used
as a terminal node of a network via which the base station can directly
communicate with the mobile station. Specific operations to be conducted
by the base station in the present invention may also be conducted by an
upper node of the base station as necessary. In other words, it will be
obvious to those skilled in the art that various operations for enabling
the base station to communicate with the mobile station in a network
composed of several network nodes including the base station will be
conducted by the base station or other network nodes other than the base
station. The term "Base Station" may be replaced with a fixed station,
Node-B, eNode-B (eNB), or an access point as necessary. The term "mobile
station" may also be replaced with a user equipment (UE), a mobile
station (MS) or a mobile subscriber station (MSS) as necessary.

[0092] The embodiments of the present invention can be implemented by a
variety of means, for example, hardware, firmware, software, or a
combination of them. In the case of implementing the present invention by
hardware, the present invention can be implemented with application
specific integrated circuits (ASICs), Digital signal processors (DSPs),
digital signal processing devices (DSPDs), programmable logic devices
(PLDs), field programmable gate arrays (FPGAs), a processor, a
controller, a microcontroller, a microprocessor, etc.

[0093] If operations or functions of the present invention are implemented
by firmware or software, the present invention can be implemented in the
form of a variety of formats, for example, modules, procedures,
functions, etc. The software codes may be stored in a memory unit so that
it can be driven by a processor. The memory unit is located inside or
outside of the processor, so that it can communicate with the
aforementioned processor via a variety of well-known parts.

[0094] It will be apparent to those skilled in the art that various
modifications and variations can be made in the present invention without
departing from the spirit or scope of the invention. Thus, it is intended
that the present invention cover the modifications and variations of this
invention provided they come within the scope of the appended claims and
their equivalents.

[0095] The present invention is applicable to a wireless mobile
communication apparatuses.

Patent applications by Dong Cheol Kim, Gyeonggi-Do KR

Patent applications by Dragan Vujcic, Limours FR

Patent applications by Hyun Woo Lee, Gyeonggi-Do KR

Patent applications by Jin Sam Kwak, Gyeonggi-Do KR

Patent applications by Min Seok Noh, Gyeonggi-Do KR

Patent applications by Seung Hee Han, Gyeonggi-Do KR

Patent applications by Sung Ho Moon, Gyeonggi-Do KR

Patent applications by Yeong Hyeon Kwon, Gyeonggi-Do KR

Patent applications in class Arbitration for access to a channel

Patent applications in all subclasses Arbitration for access to a channel